Singularity

Some sizeable ups and downs more or less equaling out anomaly wise; 10.7*C is my guesstimate for this month .

Ugh. Just caught up on this as I'm on holiday... well let's just say sometimes it's not nice at all to have called something right; my points a couple of days ago about the underlying structure concerning me have unfortunately proved highly applicable to this particular TC (I've seen a few break the rules in seasons past). It just seems that once a broad rotation with some spiral banding establishes, any system that is expected to encounter more favourable conditions ahead of it than were in place during the establishment of structure is liable to intensify rapidly unless a combination of dry air and moderate-to-strong wind shear can tear into its core. We had the former two days ago but wind shear was insufficient to drive that into the core of Maria. So it is that we are again faced with a destruction-laden recent past and events equally or perhaps more so to come depending on whether Maria weakens much (if at all) before then next landfall (assuming no major deviations from NHC guidance on track). There may be an EWRC getting underway at the mo. If so the duration will be important - worst case scenario is a fast replacement leaving time for full utilisation of oceanic heat content plus low shear and decent humidity prior to landfall, having expanded the wind field during the EWRC. Here's hoping such efficiency is not achieved.

Well I don't like the look of this one bit; with very favourable conditions for development likely over the next 4-5 days, all Maria had to do was sort out a good structure and based on the past few hours of satellite imaginary that's just what has happened. The 'wrapping-up comma' shape is a bad omen. Given model limitations and what happened with Irma I'd not be surprised to wake up to a hurricane tomorrow that then steadily marches toward major status over the following day or two. The best possibility for this not to occur is if the low level centre is now as well aligned with the mid-level as would be expected in the current low-shear environment. Back in the seasons 2013-15 this was almost a given (oddly so) but this year is playing by very sifferent rules so I'd go as far as to call it a minor miracle if it turns out to be the case. Worst part of all this is, even a low-end hurricane will be a lot of trouble if it tracks across the northern Leewards and co. Small chance based on typical modelling errors of a track further south and then on to the NW Caribbean... but then the likes of Florida come under threat which is also very troubling. There's been too many of these 'ominous evenings' this season... and we're only halfway through the climatological duration!

Good luck to them all. I'm going to peel myself away from this for a while... it's been quite the day (and week, in fact fortnight!) for tracking tropical cyclones.

Good point, for some reason I lost the ability to see blue colours for a moment there but yes, if it continues, it's bad news in big ways.

Scary. This sort of thing is why I said 'overall' impacts earlier... for every winner there's usually a loser

Well I'll be the first to say - OUCH Jose, that looked like it hurt! Interesting to see the eyewall evidently refusing to back down; that's an impressive wrap-around of very cold cloud-tops over the past hour. Trying to use the extra ventilation to it's benefit and this I imagine is why the models expect Jose to remain a hurricane while waiting for conditions to improve again - quite possibly while undertaking a large anticyclonic (i.e. clockwise) loop as a ridge passes to the north in between two deep troughs and then the western trough interacts with the remnants of Irma to produce a 'weakness' toward which Jose is likely to venture - in this way placing the East U.S. coast at risk of impacts. Just a possibility, but one the models are surprisingly keen to explore given the complexity of the sequence required to get there.

As bad as things are, the track Irma has taken has actually been among the best-case scenarios in terms of minimising the overall wind and surge impacts. That they're still severe in so many places really puts the scale of the hurricane into perspective. It's always sad to see a once magnificent ocean-faring tropical cyclone turn ugly (usually quite literally due to terrain interactions) and impact land areas - let alone multiple land areas or in this case about a dozen (if all islands are counted separately). Hopefully Jose can simply be a handsome, long-lived out-to-sea 'cane. Oh wait, it just got hit by some wind shear pretty hard... oh well! Anyway - thoughts are with the countless populations currently suffering as a part of Irma's final chapter. Stay strong, Floridians.

So the outer eyewall didn't entirely collapse after all... I'm amazed and yet not as surprised as I'd be with nearly all other storms. Makes me wonder if the battle for supremecy will again be seen, and whether the peak winds will again manage cat 5 status more often than not regardless. The frequent EWRC-like cyclesare one of the main reasons Irma has become so huge. That and the particularly abundant atmospheric moisture across many days of its lifetime.

Interaction with Cuba has taken out the large outer eyewall that was periodically competing with the inner one and causing fluctuations in intensity similar to what EWRCs would bring but more frequently. My concern now is that the freed up, tighter inner eye may be able to respond more rapidly to improved oceanic heat input than the old larger eye would have been. That the small eye has managed to stay just offshore increases the probability of this. If it happens, a relatively small but significant region will be under threat from a cat 4 or 5 landfall impact while the broader storm may have winds more akin to a cat 1 or 2 following the degradation of structure this morning. With or without an intense eye, though, the storm surge will still be very extensive and of cat 5 magnitude due to the inertia of water-buildup brought about by Irmas prolonged period spent in a very deep and intense state. So this remains the primary concern as others have been pointing out.

Not often I've been able to pick out the concentric eyewall structure on standard-resolution infra-red but that's just what can be done at the moment. The old inner eyewall has been very stubborn but I think it's finally losing the battle. Also, the eye jogged north in the past hour, reducing the likely duration of direct interaction with Cuba. Every little bit more latitude helps Irma and Cuba... and really doesn't help Florida. Unless the unthinkable happens and Irma stays so far south that the trough doesn't lift it north properly... but the odds on that look pretty slim given that it's been pretty much dead-on the NHC track over the past day.

Well this one really is an over-performer... in fact I can't quite believe my eyes here; this 'whippy' effect to the CDO on infra-red has in my experience been associated with peak sustained winds exceeding 180 mph but I wonder if in this case the CDO as a whole just happens to be spinning pretty fast relative to the eye. Either that or Jose is Irma-slim .

I did consider that too, but over the Category 6 WU blog there's been a lot of comments stating that they're too far apart for the relatively small Katia to have much direct impact on the movement of Irma. One other thing I've been wondering - given the potential for the storm surge to coincide with a spring high tide - is whether the sheer mass of Irma might slow the onset of northerly motion following the stall-and-turn, but I expect if so, the models are already factoring this in to the timing of events.

Hurricane Katia, now up to 90 mph and with room for further strengthening before landfall in Mexico, is complicating matters as its outflow may impact the southern portion of the trough that's expected to turn Irma north, but the extent and nature of that impact seems to show little agreement between models, with this not being helped by the fact that Katia has been exceeding projected model intensities. Given recent trends, the overall signal appears to be that a stronger Katia affects the trough in a manner that delays the turn north of Irma, but I can't be entirely sure of this so please take it as just a suggestion rather than statement of fact.

Typical... the moment Irma is taken a whisker below category 4 strength, deep convection wraps neatly right around the eye... as if in angry retort! It will be interesting to see how much impact Cuba's high mountains along the eastern-south coastline have on the storm. Every moment the storm moves west increases the likely impacts of Cuba as a whole of course... and of Irma on Cuba. It's unfortunate that the most direct impacts look to occur across the lowest-lying central parts of Cuba but what can you do. I must say, Irma's done a great job of threading between most of the Bahamian islands. If it wasn't such a massive storm that would have really kept the damage down. I sure hope the pattern changes by October in favour of cyclones staying out at sea - not that I'm seeing many signs of that in the longer-range at the mo...

Not exactly on the way there, but I get what you mean by where it ends up; It does look pretty 'circumstantial' though; the trough-ridge sequence has to be just-so for such a loop to take place.

Possibly a two-faced analysis is appropriate this morning as Irma's eyewall has become less symmetrical but at the same time the CDO has recovered on the western side such that the braoder structure is more symmetrical. As such one could conclude that if the eyewall sorts itself out again within the next few hours, another round of strengthening is likely to take place. Whether that'd be to more than 185 mph it remains to be seen. Heat content increases for the storm over the Bahamas, but so does land interaction, albeit to a very minor extent. I've not been able to locate a wind shear forecast as my usual sources have been inundated with impact-related discussions (understandably so). I expect I'm not alone, though, in suspecting that the true peak winds edged nearer 190 or so for a time during the dip in pressure sub-910 mb. It depends of course on how the surrounding pressure environment has changed, if at all; higher than usual pressure around the storm has allowed for stronger winds than usual relative to core pressure so if that conditions has subsided at all, the dip in pressure will have been balanced against with winds not peaking above the 185 figure. It does appear that the NHC have been running with, supported by recon data where possible. I want to believe that the storm has hit its lifetime peak and will not pack quite such an extreme punch for the Bahamas, but storms like Joaquin of recent years indicate that a second peak in Irma can't be ruled out at this time. Fingers crossed it doesn't come to pass.

Never mind the translation; the point is clear enough. That's a very low pressure to experience first-hand by those who are still on the island.

Looking at this, Irma has actually performed a wiggle sufficient to place St Barth's in the northern eye wall. Talk about tough luck! That bit of westward movement certainly unnerved some in PR but a NW movement does look to have resumed now, albeit based on only the last two frames. In terms of the eye and CDO as a whole, there seems to be a bit of a balancing act going on between increased mid-level wind shear and increased available energy from the waters; the CDO has become slightly elliptical but the intensity of convection has increased slightly to compensate. As a result, the storm is officially maintaining peak sustained winds of 185 mph despite a less than optimal structure. Should wind shear relax again any time soon then we could see that run at 190 mph+ depending of course on the timing of EWRCs - one of which the storm appears to be gradually approaching as the eye has slowly been shrinking during the past few hours.

I am struck obviously by the extraordinary form of Irma first but then also the extensive convective activity elsewhere in the basin with 13L now in the GOM and Jose consolidating more in the MDR. Ahead of Irma lies plenty of moist and unstable conditions plus higher oceanic heat content than is currently on tap. So... what's to limit this hurricane apart from eye wall replacement cycles and land interaction? Speaking of the former, the latest effort seems to have become stuck in a concentric eyewalls situation; As for the latter, maybe some interaction of the CDO with PR & later Dominica but the model tracks generally keep the eye itself from taking much of a hit, if any. So it comes down to Cuba's mountainous southern side (particularly SE corner) but here I wonder if there could be some degree of 'density forcing' whereby air piling up against the mountains on the leading side of the cyclone achieves a high enough density to force more of a northward component to the cyclone's movement than would otherwise occur. It's debatable whether this is actually physically possible, particularly with such a large cyclone, but over the past decade I've seen a few cases here and there that at least suggest the possibility exists. At this time a consensus between ECM and GFS (wide margins though!) would avoid all that much interaction with Cuba's mountains anyway, in which case Floridians will be in desperate need of the storm turning north as far east as possible. As wacky as GFS seems with the movement of the storm, at least it allows for some hope that the best-case scenario of a turn before Florida is not without chance. Unfortunately this still sees the Bahamas taking a serious beating unless something highly unforeseen knocks the cyclone's core strength down a fair way. For all we know though, a stronger than expected development from TD 13 could change the game yet again by eroding a weakness in the ridge west of Florida and opening the door to the GOM for Irma. I am disappointed to have reason enough to write that last sentence but there it is . Oh and the official dropsonde reading is 920 mb which is still 6 mb lower than found during the last flight just a few hours ago - so a steady rate of deepening continues. To be honest given all that's before me at the moment, I'd be more surprised if Irma didn't reach that most horrific benchmark of 200 mph sustained winds, to this date in history not managed by any Atlantic-basin hurricane. Therefore I sincerely hope to be as surprised as possible when I catch up on things tomorrow morning!

Such variety in the model output but I can just about pick out a predominant warm signal for maybe half the month. An uncertain 15.2*C is my guesstimate.

A horrific storm and what a shame that something so magnificent to look at from space has behaved in such a catastrophic fashion. Currently I am watching with a resigned sigh as the dry slot that tried to take the storm down becomes increasingly moist as a result of the sun getting to work on the vast areas of anomalous surface water across the region. As the centre drifts over the bay, we have to hope that it does not gain enough independence from the nearby boundary line to become able to establish its own more vigorous circulation within the increasingly moist central airmass. Meanwhile, (briefly OT here), Potential Tropical Cyclone Ten is streaming a lot of upper-level moisture out across the N. Atlantic. Good job the polar jet looks to steer most of that north of the UK during the coming week.

Oh yes I am interested Frosty It's enjoyable to watch the models back down from the initial assumptions of tropical cyclones simply adding extra oomph to the polar boundary and bringing about a flat westerly pattern such as would most likely result given the coupled-positive AO & NAO pattern evident in the N. Hem view of the charts. What we see being picked up on instead is a 'mangling' of the jet pattern by the areas of particularly warm air that are moved poleward by the tropical cyclones; this forces poleward arcing of the jet stream where it would not otherwise have occurred, essentially amplifying the overall pattern. When you have a positive NAO, amplification often sees ridges moving NE from the Azores. Granted, this depends on those tropical cyclones being well-developed enough to move a sufficient amount of warm air poleward. Should either of the two systems visible in the first and second of the N.Atlantic-view ECM charts posted above - which incidentally display more of a subtropical or hybrid form than tropical, particularly the one near Newfounland which is having a go at impersonating Hurricane Sandy of five years ago - turn out to be weaker, we may yet see the simpler boosting of the jet stream take place after all. This would require all of ECM, UKMO, GEM and GFS to be wrong, which is unlikely in the first case at 3 days range, but at 6 day's range is not out of the question. So perhaps a cutting-short of the settled spell compared to the latest consensus... but then again we could just as easily get lucky and drift joyously into mellow fruitfulness .

So much upstream complexity at the moment as the La Niña-like signal from those strong C Pac traded propagates across to the subtropical Atlantic but then gets distorted majorly by numerous tropical or subtropical systems, so changing what we find ourselves dealing with here in the U.K. There does tend to be a net effect in September of sending warm air aloft over NW Europe which help build ridges of HP there. Trouble for us is this is achieved via enhanced zonal flow so a strong jet running west-east with a distinct dividing line over the UK that can easily lie anywhere between Southampton and Edinburgh and occasionally as far as the northernmost reaches of the UK. Sometimee though, the divine tendency to the jet that the La Niña-like signal encourages can form a sort of treaty with the NW Euro ridge signal such that lows keep dropping down a little way SW of the UK. Unfortunately those lows rarely get stuck there with such an active jet unless they can be totally cut off such as UKMO and GEM spent a few days toying with the idea of recently. So they typically drift across the UK after a day or two with scope for some large rainfall totals. So I suspect there will tend to be an often quite warm but muggy state of affairs at least here down south for the next week or two, with a few heavy doses of rain to contend with but a reasonable are amount of dry and usable weather in between. I wish I could say the same for those at the other end of the UK. You're not without a change but it's a pretty slim one.

I'd never back GFS/GEFS over a combination of UKMO and ECM hence my interest in the ECM output but given the GEM 12z I had a feeling it would edge back toward a warmer and more settled outcome - and so it has, albeit a little tenuously. It manages to cut-off the low which is essentially what GFS has little interest in, but that low is a bit deeper and further north, which leaves us in a less certain state of improved weather conditions, despite the broader pattern being very similar; This run goes on to keep the jet a bit flatter than the 00z which makes a lot of difference to conditions across the S. half of the UK. This sort of thing - to answer @knocker's inquiry - being where the UKMO 12z differs notably from the ECM 00z; it has a flatter jet stream passing to the N of the UK, even more so than this 12z ECM has produced. It's not that big a difference on the face of it, but fine margins look to be at play with respect to the divide between warm/very warm weather with the odds favouring not much more than some diurnal shower formation and cooler, cloudier weather with a risk of spells of rain. It's not ideal by any means and we sure could do with the even flatter jet of the UKMO 12z, but (at least some) southerners may find it a satisfactory recovery in temperatures at least. Meanwhile Central Europe appears well placed for a late summer heatwave of considerable intensity for the time of year. As I'm paying a visit to the Balearic Isles in mid-September, seeing the 25*C 850 hPa isotherm edging toward there at the end of August does make me wonder what sort of overnight temperatures I might have to face given the warming effect on an already much warmer than usual Mediterranean. Of course with the knowledge of my time away in mind, it's probably wise to prepare for (relatively) exceptional heat to visit the UK in just under a month's time .